High voltage regulator-switch for bi-layer kinescope



July 11', 1967 R. A. GUILLETTE 3,330,990

7 HIGH VOLTAGE REGULATOR-SWITCH FOR BI-LAYER KINBSCOPE Filed Sept. 8, 1964 3 Sheets-Sheet l SWITCH oaa 00000 SQUARE WAVE TARGET 2o 7 f VOLTAGE we-MESH (KV) lo 42.5

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O I l/ ATTORNEYS United States Patent 3,330,990 HIGH VOLTAGE REGULATOR-SWITCH FOR BI-LAYER KINESCOPE Robert A. Guillette, Methuen, Mass., assignor to Polaroid .Corporation, Cambridge, Mass., a corporation of Delaware Filed Sept. 8, 1964, Ser. No. 394,900 Claims. (Cl. 315-31) This invention relates to power supplies for color television kinescopes of the type having a viewing screen made up of a plurality of superposed cathodoluminescent layers, and more particularly to a power supply capable of switching the accelerating voltage on the screen between levels sufficiently far apart to insure selective excitation of the layers.

It is well known that the radiant output from a screen made up of a plurality of superposed cathodoluminescent layers due to an impinging beam of electrons is determined by the energy of the beam. With a conventional trilayer screen, a low value of accelerating voltage will limit penetration of the beam to the layer closest to the gun causing only such layer to be substantially excited; a higher value of voltage will limit penetration to the intermediate layer causing only the latter to be substantially excited; and a still higher value of voltage will permit penetration to the outermost layer causing only it to be substantially excited. When the kinescope is constructed to operate on the conventional three primary color system, the three layers would be red, blue and green. In operation with a single electron gun, the red video signal would be applied to the gun during the time the accelerating voltage Were such that the beam excited the red layer, the blue video signal would be applied to the gun during the time the accelerating voltage were such that the beam excited the blue layer, etc.

This requires the sequential switching of thousands of volts on the screen, usually at the field rate with the result that red, blue and green fields of the corresponding color-separation images of the scene being televised are sequentially reproduced on the viewing screen, and the scene appears in full color. Typical values of voltage necessary to achieve the three required colors are listed in US. Patent No. 2,566,713 granted Sept. 4, 1951 to V. K. Zworykin as 10 kv., 25 kv. and SOkv. It is the reliable switching of voltages of this order of magnitude and at the field frequency with minimum power requirements that is the problem to which the present invention is directed, and the provision of novel apparatus to achieve such reliable switching is the primary object of the invention. Another object of the invention is to provide novel apparatus by which the voltage on a mesh positioned closely adjacent the screen can be easily modulated in synchronism with the switching of the accelerating voltage for the purpose of eliminating misregistration between color-separation images reproduced on the screen.

Basically, the invention involves the use of a flybacktype high voltage supply similar to that used in a conventional kinescope to develop the so-called picture-tube or target voltage. In such type of supply, the large voltage pulses induced across the horizontal deflection coils of the kinescope during the horizontal retraces of the electron beam are stepped-up, rectified and filtered to develop the target voltage. This voltage is maintained at a substantially constant value by the use of a shunt voltage regulator tube, generally a triode, to whose grid is applied a fraction of the high voltage related to a reference voltage. Any tendency of the voltage to change from its nominal value, in response to changes in the load relative to the reference, is opposed by a compensating change in conduction of the tube with the result that the target voltage remains substantially constant at its nominal value.

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The concept on which the present invention is based is the recognition that the nominal value of the target voltage is dependent upon the value of the reference voltage, which, in conventional regulator systems, is ground. When the reference voltage is changed suddenly, the regulator circuit causes an inverse change to occur in the nominal value of the target voltage with the result that the regulator circuit acts like a switch in response to sudden changes in the reference voltage. Upon stabilization of the regulator circuit, which occurs in a period of time small in comparison to the line time, the regulator circuit again acts like a regulator, but one which is effective to maintain the target voltage substantially constant at its new nominal value. By varying the reference voltage at the field frequency, the regulator tube is effective to switch the target voltage between different nominal values at the field frequency, while still being effective to stabilize the target voltage at its nominal value during the frame time. Thus, the modulation of the reference voltage with a wave of proper amplitude and frequency causes the target voltage to switch in the manner desired.

The more important features of this invention have thus been outlined rather broadly in order that the detailed description thereof that follows may be better understood, and in order that the contribution to the art may 'be better appreciated. There are, of course, additional fea-' tures of the invention that will be described hereinafter and which will also form the subject of the claims ap-j pended hereto. Those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for designing other structures for carrying out the several purposes of this invention. It is important, therefore, that the claims to be granted herein shall be of sufiicient breadth to prevent the appropriation of this invention by those skilled in the art.

In the drawings:

FIGURE 1 is a schematic representation of a colortelevision system utilizing a bi-layer kinescope that operates on the red-white theory of color;

FIG. 2 is a representation of the time variation of the voltages on the screen and on the registration-correction mesh of the kinescope of FIGURE 1 and showing the proper video signal sequence necessary to reproduce the scene being televised in color using the red-white theory of color;

FIG. 3 is a combined block diagram and circuit for showing details of the power supply; and

FIG. 4 is a series of plots showing the waveform of various voltages developed in the circuit of FIG. 3, and the corresponding video signal sequence.

The .present invention is illustrated in a color television system which utilizes the red-white system of color analysis disclosed in application Ser. No. 297,341, filed July 24, 1963, now Patent No. 3,289,775 and assigned to the same assignee as the present application, although it should be understood that the present invention is also applicable to a color television system which utilizes the more conventional red-blue-green system of color anlysis such as disclosed and claimed in US. Patent No. 2,566,713 to Zworykin granted Sept. 4, 1951. In the red-white system of color analysis, only two color-separation images of the scene being televised are necessary: namely the red and the green, or the relatively long and relatively short dominant wavelength color-separation images. The red and green video signals, individually characterizing the red and green color-separation images, can be used to sequentially modulate a single electron beam such that the red color-separation image is reproduced on a viewing screen in red light (that need not necessarily match the color of the red color-separation image), and the green color-separation image is reproduced in achromatic or white light. A viewer of the sequential reproduction of the red and green images in red and achromatic light respectively sees the scene being televised in full color even though each picture element of the viewing screen emits only red or achromatic light.

A television system based on the above-described system of color analysis is shown in block diagram form in FIGURE 1 and is designated by reference numeral 10. System includes transmitting apparatus 11, transmission channel 12 and receiver apparatus 13. Transmitting apparatus 11 is constituted by camera 14, which views the scene being televised separating at least the red and green components, and producing a least a red and a green video signal which is applied to encoder 15 preparatory to transmission to receiver apparatus 13. Encoder 15, by conventional means (not shown), adds the synchronizing information to the two channels carrying the video signals and prepares the latter for application to transmission channel 12. The latter may be an RF link or a coaxial cable depending upon factors not related to the present invention.

Receiver apparatus 13 includes decoder 16, bi-color kinescope 17 and receiver circuitry 18. Decoder 16 operates on the signals furnished by transmission channel 12 to recover the red and green video signals, which, it will be recalled, are independent signals individually characterizing the red and green color-separation images of the scene being televised. Decoder 16 also applies the synchronizing information to conventional sync separator 19 which supplies the vertical sync pulses to vertical deflection generator 20 and the horizontal sync pulses to horizontal deflection generator 21. Generators 20 and 21 produce outputs which are applied to deflection means 22 of kinescope 17, the latter including at one end, a viewing screen 23 having a covering thereon that constitutes a target for a beam of electrons produced by electron gun means 24 at the other end of the kinescope. As a result of the periodic deflection signals, the electron beam is caused to scan the target in accordance with the deflection signals to define a conventional raster. The covering on screen 23 may be constructed in the form of two superposed layers of cathodoluminescent material 25, one of which emits red light and the other of which emits minusred light under electron excitation. When the red lightemitting layer is closer to the electron gun, the screen will emit only red light if the kinetic energy of electrons impacting the screen has some lower value such that penetration is limited to this layer. Thus, a portion of the red color-separation image can be reproduced on the screen by modulating the intensity of the beam with the red video signal during a portion of the periodic scan of the screen by the beam. However, the screen will emit achromatic or white light if the kinetic energy of electrons impacting the screen has some higher value such that the beam penetrates both the red and the minus-red layer and excites both to substantially the same degree. Thus, a portion of the green color-separation image can be reproduced on the screen by modulating the intensity of the beam with the green video signal during another portion of the periodic scan of the screen. When odd-line interlaced scanning is used, one field of the raster is in red light interlaced with the other field in achromatic light; and a satisfactory reproduction of the scene in full color is achieved.

To this end, the vertical sync pulses, which appear at the field frequency may be utilized to synchronously control two electronic switches, designated schematically at 26 and 27. Switch 26 is associated with the two video outputs of decoder 16 and sequentially applies only one of such outputs at a time to the control grid of electron gun means 24 whereby the intensity of the beam can be modulated sequentially, by either the red or green video signals. Switch 27, on the other hand, is associated with highvoltage supply 29 which produces a relatively high voltage and a relatively low voltage (their orders of magnitude being 20,000 and 10,000 volts respectively) which are individually available to be applied sequentially via switch 27 to a conductive layer (not shown) on material 25, the relatively high target voltage causing simultaneous and equal excitation of both layers of the screen to produce white light, and the lower target voltage causing excitation of only the layer closer to the gun to produce red light.

To synchronize switches 26 and 27, square Wave generator 28 driven by the vertical sync pulse produces a square wave at the field frequency (30 c.p.s.). As shown in FIG. 2, during one field scan, the output of generator 28 is such that switch 26 applies the green video to gun 24 when switch 27 applies the larger target voltage to material 25; and half of the green color-separation image is reproduced on the viewing screen in achromatic light. During the next field scan, the output of generator 28 is such that switch 26 applies the red video to gun 24 when switch 27 applies the smaller target voltage to material 25; and half of the red color-separation image is reproduced on the viewing screen in red light interlaced with the half of the green color-separation image reproduced in achromatic light. In other words, the above-described apparatus presents the two primary colors (red and white) on a field sequential basis wherein the lines of the raster associated with one field scan are always red and the lines of the next field scan are always achromatic. It will be apparent from the following description, however, that the present invention is applicable to any other system of presentation such as frame sequential, etc., as well as to a system using more than two primary colors.

The sequential interlaced reproductions of the scene being televised will best present the latter to an observer in substantially full color (even though each elemental area of the viewing screen emits only red or white light) when the interlaced reproductions are in optical registration. As is well known in the art, the switching of the target voltage to achieve selective color control results in modulation of the raster size since the field produced in achromatic light (requiring the higher target voltage) will be smaller in area than the field reproduced in red light (requiring the lower target voltage), assuming that the sweep signals are not compensated. While compensation of the sweep signals is theoretically a possibility, an expedient which is much simpler, is the provision of an electron permeable mesh, designated by reference numeral 30, between gun means 24 and material 25 on the screen. Mesh 30 is physically close and parallel to the surface of material 25 but electrically insulated therefrom. As indicated in copending application Ser. No. 344,914, filed Feb. 14, 1964 and owned by the assignee of the present application, the modulation of the voltage on mesh 30 in synchronism but out-of-phase with the modulation of the accelerating voltage achieves the desired result of reducing misregistration between the reproduced colorseparation images to a minimum. In a model of the device shown in FIGURE 1 and disclosed in the aforementioned copending application Ser. No. 297,341, filed July 24, 1963, material 25 is constituted by a granular layer of minus-red light emitting phosphors on viewing screen 23, and a granular layer of red light emitting phosphors superposed thereon and closer to the electron gun, the red light emitting phosphors being uniformly distributed over but covering less than of the screen and being separated from the minus-red light emitting phosphors by a nonluminescent barrier layer: 10 kv. applied to material 25 is sufiicient to excite only the red light emitting phosphors with interstitial electrons of this energy being stopped by the barrier layer, and 20 kv. is sufiicient to excite both the red and minus-red light emitting phosphors into emission of achromatic light. In such case, good registration is obtained when the mesh voltage varies by about 1600 volts peak-to-peak about an average value of approximately 12.5 kv. in the manner shown in FIG. 2. To achieve this, the requisite mesh voltages are obtained from supply 29 and applied individually and sequentially to mesh 30 by mesh voltage control 31, the operation of which is also synchronized by the output of generator 28.

The novel apparatus bywhich to achieve, with a minimum power expenditure, both reliable switching of the thousands of volts necessary to selectively excite material 25, and proper modulation of the voltage on the mesh to insure the desired registration, is shown in FIG. 3 to which reference is now made. As indicated previously, the output of decoder 16 is applied to sync separator 19 so that the vertical sync pulses are applied to vertical deflection generator 20 and the horizontal sync pulses are applied to horizontal deflection generator 21. Generator 20 may be conventional and would thus include vertical oscillator circuit 32, synchronized by the vertical sync pulses provided by sync separator 19, and vertical output circuit 33 which causes a substantially linear sawtooth current at the field frequency to pass through vertical coil 34 that constitutes a portion of the deflection means 22 of the kinescope. Likewise, generator 21 may be conventional and may thus include horizontal oscillator 35 AFCd with the horizontal sync pulses and producing a sawtooth voltage at the line frequency which is applied to horizontal output circuit 36. The latter is coupled to autotransformer 37 across which the horizontal coils 38 of the deflection means of the kinescope are connected so that a substantially linear sawtooth current at the line frequency passes through horizontal coil 38 that constitutes another portion of means 22. At the termination of each sawtooth pulse, the current supplied to coil 38 is cut off and the collapse of the magnetic field in the coil causes the latter and its associated components to ring at a relatively high frequency. Only'one half a cycle of oscillation is permitted to occur due to the provision of damper diode 39 which begins to conduct at the end of the half cycle and places a low resistance across the circuit permitting the current through the coil 38 to begin to increase again in a substantially linear manner in response to the next sawtooth pulse. When the diode conducts, the rectified pulse is filtered by capacitor 40 and added to the nominal B+. This No. 1 boosted B+ provides the necessary voltages for operation of the components of the sweep circuits, etc. Generators 20 and 21 are shown schematically since they are essentially conventional and it should be realized that the various adjustments usually provided for vertical and horizontal size and linearity control are not shown in order to simplify the drawing.

As indicated previously, high voltage supply 29 must furnish the two voltages necessary to selectively excite the two layers of material 25 in the proper manner, as well as-the voltages for the mesh. A fiyback-type of power supply is utilized, and in order to isolate the horizontal sweep circuits from the effect of switching the target Voltage and modulating the mesh voltage, supply 29 has a first portion from which the two target Voltages are obtained; and a second portion from which the mesh voltages are obtained. The first portion of supply 29 is associated with horizontal coil 38 and is quite similar to a high-voltage section of a horizontal deflection system found in conventional three-color kinescopes of the shadowmask variety in that such portion includes horizontal drive circuit 41;'horizontal output circuit 42; autotransformer 43; energy storage coil 44, which simulates the horizontal coil; high voltage rectifier tube 45; and regulator tube 46. Circuit 41, being coupled to coil 38, produces a sawtooth voltage synchronized with the input to circuit 36 of horizontal deflection generator 21, and such voltage when applied to circuit 42 causes a sawtooth current to flow in energy storage coil 44, Damping diode 47 associated with coil 44 functions in connection with this coil just as diode 39 functions in connection with coil 38. Capacitors 48 and 49 together with resistor 50 provide a No. 2 boosted B at a level sufliciently high to supply various components of the receiver, one of which is mesh voltage control 31. High voltage rectifier 45, connected to the top of autotransformer 43, rectifies the large voltage pulses produced in the transformer each time the current through coil 44 is suddenly cut off at the termination of the horizontal traces. After rectification, the pulses are filtered by the capacitance of the target to ground, to provide a high-voltage D.-C. output (the so-called target voltage) whose value is determined by the turns ratio of the transformer and the operation of regulator tube 46. The purpose of regulator tube 46 is two-fold: l) to maintain the high-voltage on the target at a substantially constant nominal value during each vertical field; and (2) to cause the high voltage on the target to switch from one nominal value to another at the field frequency such that the desired selective excitation of material 25 is achieved.

The target voltage must be maintained substantially constant during each vertical field because bright picture elements on the viewing screen require a high beam current and would impose a severe drain on the power supply that tends to lower the target voltage thus tending to reduce the brightness and interfere with proper color control; and dark picture elements require a low beam current that tends to cause a rise in the target voltage thus tending to increase the brightness and likewise interfere with proper color control. In order to maintain the target voltage substantially independent of the load as determined by the brightness of the individual picture elements, tube 46 is connected as a shunt regulator across the load (since the regulator must permit reverse current to flow when the beam causes secondary emission to occur at the target) by connecting the plate of tube 46 to the cathode of rectifier 45, and connecting the cathode of tube 46 to B. A fraction of the target voltage, namely the No. 2 boosted B+ is applied to the grid of tube 46 through a grounded high resistance network 52, 53, 54 so that, in effect, the voltage at the grid is dependent upon the No. 2 boosted 13+ and the voltage at point 55.

Square wave generator 28, synchronized with the vertical sync pulses, produces a square wave of amplitude E at the field frequency, and this wave is coupled through capacitor 56 to diode 57 so that the reference point 55 is clamped negatively to ground as shown in FIG. 4(a). During the field scan that the output of generator 28 is positive, point 55 is efiectively at ground potential; and the voltage at the grid of tube 46 has some preselected value relative to the cathode voltage such that the tube conducts, drawing plate current furnished by rectifier 45. When the electron beam scans an elemental area which is to be dark and the beam current decreases, the voltage at the cathode of tube 45 tends toincrease. Simultaneously, the No. 2 boosted B+ tends to increase, and in turn, tends to cause tube 46 to conduct more heavily. This opposes the tendency of the voltage at the cathode of tube 45 to increase, and thus holds down the target voltage stabilizing the latter at a nominal voltage (in this case 10 kv.).

When the output of generator 28 swings negative, point 55 follows thus changing the bias on tube 46 in such a Way that conduction abruptly decreases causing an increase in the target voltage to another nominal voltage higher than the nominal voltage when point 55 is at ground potential (in this case, the parameters are chosen so that the higher nominal voltage is 20 kv.). The output of generator 28 remains negative for a complete field scan, during which time tube 46 again functions as a voltage regulator. At the termination of the negative pulse from generator 28, the tube functions as a switch and the target voltage I abruptly switches to its lower nominal value in a sequence related to the output of the generator as shown in FIG. 4.

The above-described apparatus constitutes the first portion of supply 29, which, it will be recalled, maintains the target voltage at a substantially constant nominal value during each field, but is also effective to cause the target voltage to switch from one nominal value to another at the field frequency. It will be recalled also that supply 29 has a second portion from which the mesh voltages are obtained. Such second portion includes rectifier 58 and cathode follower 59 whose output is connected to mesh 30. Rectifier 58 operates, in connection with the 10 kv. to kv. square wave applied to the target, just like rectifier 45 operates in connection with the voltage pulses produced by transformer 43 and coil 44. That is to say, the target voltage square wave is rectified by tube 58, filtered at 60 and applied to the plate of cathode follower 59. In the preferred embodiment shown, this places about 14 kv. on the plate of the cathode follower. The grid of the cathode follower is connected to the output of rectifier 45 through resistor 61 and to ground through resistor 62. In addition, the grid is connected through 'high voltage capacitor 63 to the plate of amplifier 64 whose load resistor is connected to the filtered No. 2 boosted B+ supply. The cathode of cathode follower 59 is connected through a large (e.g., 50 megohm) resistor to ground to provide a path for the flow of bias current. When the order of magnitude of each of resistors 61 and 62 is about 100 megohms, with resistor 62 being about twice as large as resistor 61, and when the plate resistance of amplifier 64 is about 1 megohm, the grid of tube 59 is essentially A.-C. grounded, which means that voltage divider network 61, 62, capacitor 63 and the plate resistor of tube '64 act as a low pass filter. Thus, the nominal voltage at the grid of tube 59 (i.e., the voltage when the input to amplifier tube 64 is grounded) will be about two thirds of the average value of the target voltage. The value of the parameters are chosen so as to place this nominal value of grid voltage at slightly higher than the lower of the two target voltages such that the nominal voltage across the cathode resistor is about 12.5 kv. As a consequence of this arrangement, the square wave input to amplifier 64 is inverted and applied to the grid of cathode follower 59 causing the voltage on the mesh to vary about the nominal value of 12.5 kv. by the proper amount (by properly positioning the voltage tap on the load resistor of amplitude 64) and with the proper phase. Cathode follower 59 is essentially a series voltage regulator whose effect on the mesh voltage is dependent on the No. 2 boosted B+ and the output of square wave generator 28.

From the above description, it can now be appreciated that the deflection means for causing the beam to periodically traverse the target and define a raster is constituted by generators 20 and 21; the flyback power supply for developing the target voltage is constituted by the elements contained in the block designated 29 in FIG. 3; and the means connected to the power supply for causing the target voltage to be switched in synchronism with the traverse of the target by the beam is constituted by the elements contained in the block designated 27 in FIG. 3. It should be noted that regulator tube 46 is common to both blocks 27 and 29, since the tube functions like a regulator during each field, and like a switch at the end of each field so that tube 46 is in effect, an electronic element that includes a control electrode and operates as switch-regulator means. The control means, by which a portion of the target voltage and a reference voltage is applied to the control electrode, is constituted by resistor network 52, 53, 54 and clamping circuit 56, 57. The drive means, by which the reference voltage is modulated in synchronism with the vertical sync pulses, is constituted by generator 28.

Since certain changes may 'be made in the above apparatus without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In apparatus of the type described:

(a) a kinescope having a target;

(b) an electron gun for producing a beam of electrons focused on said target;

(c) deflection means for causing said beam to pcriodically traverse said target and define a raster;

(d) a flyback power supply associated with said deflection means for developing the target voltage for said target; and

(e) means connected to said power supply for causing said target voltage to be switched between at least two different levels in synchronism with the traverse of said target by said beam and for stabilizing said target voltage during intervals between switching thereof.

2. Apparatus in accordance with claim 1 including an electron permeable mesh interposed between said electron gun and said target and wherein said last-named means causes a registration voltage to be applied to said mesh, sai-d registration voltage being modulated in synchronism with the switching of said target voltage.

3. Apparatus in accordance with claim 1 wherein said means connected to said power supply comprises:

in a flyback power supply of the type having a high voltage rectifier:

(a) a regulator-switch electron tube having a plate, a cathode and a grid, said plate being connected to the output of said power supply, and said cathode being connected to a first reference voltage;

(b) means to couple a fraction of the output of said power supply to said grid;

(c) a resistance network connected to said grid;

and

(d) a clamping circuit for clamping said resistance network negatively to a second reference voltage.

4. For use with apparatus that includes: a cathode ray tube with a target; an electron gun for producing a beam of electrons focused on said target; and deflection means for causing said beam to periodically traverse said target and define thereon a raster made up of a plurality of traces; and wherein said target is constructed and arranged to produce different types of light in response to the switching of the accelerating voltage on the target relative to said gun from one value to another; a flyback power supply associated with said deflection means for generating said accelerating voltage, comprising:

(a) a high voltage rectifier element for producing a high voltage flyback pulse at the termination of each trace;

(b) capacitor means coupled to said rectifier element to said target for smoothing the flyback pulses to develop said accelerating voltage;

(c) a voltage regulator element connected in shunt with said capacitor means and including a control electrode, said regulator element being constructed and arranged so that the degree of conduction thereof determines the magnitude of said accelerating voltage, and the voltage at said electrode controls the degree of conduction of said regulator element;

(d) means for applying a fraction of said accelerating voltage and a reference voltage to said electrode so that a tendency for said accelerating voltage to change relative to said reference voltage tends to change the degree of conduction of said element such as to oppose such tendency and thereby stabilize said accelerating voltage relative to said reference voltage; and

(e) means to modulate said reference voltage for causing said accelerating voltage to .be switched from said one value to said other.

5. A flyback power supply in accordance with claim 4 wherein said reference voltage is switched from one level to another after the termination of a predetermined number of traces of said beam.

6. For use with a television receiver that includes: a kinescope having a target, an electron gun for producing a beam of electrons focused on said target, and deflection means responsive to horizontal and vertical sync signals for causing said beam to perodically scan said target and trace a plurality of horizontal lines that define a raster; and wherein said target is constructed and arranged to produce different types of light in response to the switching of the voltage on the target relative to said gun, between at least two different values; a fiyback power supply associated with said deflection means for generating the target voltage, comprising:

(a) a high voltage rectifier element for producing a high voltage fiyback pulse during the horizontal retrace time of the scan;

(-b) means coupling said rectifier element to said target and effective to smooth the fiyback pulses for developing said target voltage; and

(c) switch-regulator means coupled to said rectifier element for causing said target voltage to be switched between said two difierent values in synchronism with the vertical sync pulses and automatically regulating said target voltage in the interval of time between switching thereof.

7. Apparatus in accordance with claim 6 wherein said kinescope is provided with an electron permeable mesh interposed between said electron gun and said target, and wherein means are provided for developing a registration voltage on said mesh in response to the operation of said switch-regulator means, said registration voltage being modulated in synchronism with the switching of said target.

8. Apparatus in accordance with claim 6 wherein said switch-regulator means comprises:

(a) an electronic element connected to the output of said rectifier element and including a control electrode, said electronic element being constructed and arranged so that the degree of conduction thereof determines the magnitude of said target voltage, and the voltage at said electrode controls the degree of conduction of said electronic element;

(b) control means for applying a portion of said target voltage and a reference voltage to said electrode so that a tendency for said accelerating voltage to change relative to said reference voltage tends to change the degree of conduction of said electronic element such as to oppose such tendency and thereby stabilize said target voltage relative to said reference voltage; and

(c) drive means to modulate said reference voltage in synchronism with said vertical sync pulses.

9. Apparatus in accordance with claim 8 wherein said drive means includes a generator for producing a square wave having a period equal to the frame time of the sync signals and synchronized with the vertical sync signals, and is coupled to said electrode through a clamping circuit.

10. Apparatus in accordance with claim 9 wherein said means for developing a registration voltage on said mesh includes rectifier means associated with said rectifier element for rectifying said target voltage, a cathode follower to whose plate is connected the output of said rectifier means and to whose cathode is connected said mesh, and low pass filter means associated with the output of said rectifier means for establishing a nominal grid control voltage on said cathode follower.

References Cited UNITED STATES PATENTS 3,284,662 11/1966 Kagan 31517 JOHN W. CALDWELL, Acting Primary Examiner. T. A. GALLAGHER, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,330,990 July 11, 1967 Robert A. Guillette It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 60, for "anlysis" read analysis column 3, line 15, for "a", first occurrence, read at column 8, lines 22 and 23, strike out "in a flyback power supply of the type having a high voltage rectifier2".

Signed and sealed this 16th day of July 1968.

(SEAL) Attest:

EDWARD J. BRENNER Commissioner of Patents Edward M. Fletcher, Jr.

Attesting Officer 

1. IN APPARATUS OF THE TYPE DESCRIBED: (A) A KINESCOPE HAVING A TARGET; (B) AN ELECTRON GUN FOR PRODUCING A BEAM OF ELECTRONS FOCUSED ON SAID TARGET; (C) DEFLECTION MEANS FOR CAUSING SAID BEAM TO PERIODICALLY TRAVERSE SAID TARGET AND DEFINE A RASTER; (D) A FLYBACK POWER SUPPLY ASSOCIATED WITH SAID DEFLECTION MEANS FOR DEVELOPING THE TARGET VOLTAGE FOR SAID TARGET; AND (E) MEANS CONNECTED TO SAID POWER SUPPLY FOR CAUSING SAID TARGET VOLTAGE TO BE SWITCHED BETWEEN AT LEAST TWO DIFFERENT LEVELS IN SYNCHRONISM WITH THE TRAVERSE OF SAID TARGET BY SAID BEAM AND FOR STABILIZING SAID TARGET VOLTAGE DURING INTERVALS BETWEEN SWITCHING THEREOF. 